Bangladesh, May 1 -- Polish Prime Minister Donald Tusk has stirred debate across Europe after openly questioning Washingtons “loyalty” to NATO. In an interview with Financial Times, Tusk raised what he called the “biggest, most important question” for Europe: whether the United States would truly honor “NATO treaties” in the event of a (hypothetical) Russian attack. While insisting he was not being skeptical about Washingtons willingness to comply with Article 5, he warned that such guarantees must be “practical,” not merely “on paper,” and even suggested that the alliance could be tested within months.

Article 5 of the NATO treaty is the alliances core collective defence clause...